1. Field of the Invention
This invention relates to methods and apparatuses for performing minimally invasive surgery, and more particularly to instruments for providing access to body tissues and performing procedures on bone structures of a patient.
2. Description of the Related Art
Spinal surgery presents significant difficulties to the physician attempting to reduce chronic back pain or correct spinal deformities without introducing additional trauma due to the surgical procedure itself. In order to access the vertebrae to perform spinal procedures, the physician is typically required to make large incisions and cut or strip muscle tissue surrounding the spine. In addition, care must be taken not to injure nerve tissue in the area. Consequently, traditional surgical procedures of this type carry high risks of scarring, pain, significant blood loss, and extended recovery times.
Apparatuses for performing minimally invasive techniques have been proposed to reduce the trauma of posterior spinal surgery by reducing the size of the incision and the degree of muscle stripping in order to access the vertebrae. One such apparatus provides a constant diameter cannula which is made narrow in order to provide a small entry profile. As a result, the cannula provides minimal space for the physician to observe the body structures and manipulate surgical instruments in order to perform the required procedures. A narrow cannula is typically insufficient to perform one level spinal fixation procedures, which requires visualization of two vertebrae and introduction of screws, rods, as well as other large spinal fixation devices.
In some cases it is desirable to provide treatment of more than two adjacent vertebrae. For example, some conditions require that treatment be made of three adjacent vertebrae, i.e., a “two level procedure.” While a narrow constant diameter cannula is typically insufficient for a one level procedure, such a cannula is completely inadequate for a two level procedure. Thus a variety of procedures and combination of procedures requires repeated insertion of multiple cannulae, which eliminates the advantages of minimally invasive procedures.